Tension maintaining device



y 2, 1967 H. LEIBER TENSION MAINTAINING DEVICE 5 Sheets-Sheet 1 FiledMay 12, 1965 INVENTOR Heinz Leiber BY M e 7% ATTORNEYS May 2, 1967 I H.LEIBER 3,317,157

TENSION MAINTAINING DEVICE Filed May 12, 1965 3 Sheets-Sheet I5 INVENTORHeinz Lei ber BY Qgmaw W ATTORNEYS United States Patent Claims Thepresent invention relates generally to a device for maintaining thetensile stress of a material which is wound on two drums and, moreparticularly, to a device for maintaining the tensile stress of amaterial stretched between two drums when winding in the form of anArchimedean spiral, for example, which may automatically result whenwinding strips and foils on cylindrical drums.

It is already known to stress strips which are Wound on drums byproducing opposite moments on the drums by means of two separateelements which are mainly electrical torque producing elements, butwhich require a continuous power supply. In order to move the strip inits stressed condition, driving and braking moments of differentmagnitudes are needed. Also, in this arrangement, the power supply ishigher than is actually needed for acceleration of the masses involvedand to overcome friction. In order to adjust the driving and brakingmoments with respect to each other, voluminous control devices arenecessary. A further disadvantage of the electrical tensioning system isthat upon failure of the power supply or interruption of the line, thetensile stress of the strip is not assured and in such an event, thedrums can move accidentally.

With this in mind, it is a main object of the present invention toprovide a device for maintaining the tensile stress of a strip which iswound on drums without the need for a continuous supply of energy.

Another object of the invention is to provide a device of the characterdescribed wherein the tensile stress of the strip wound on drums can bemaintained while the arrangement is at a standstill as well as duringrewinding at any speed.

A further object of the invention is to provide such an arrangementwhich does not exert any power exteriorly of the system and for whichonly a small driving motor need be provided for overcoming the momentsof acceleration and friction which occur.

These objects and others ancillary thereto are accomplished inaccordance with preferred embodiments of the invention wherein twoconical rope pulleys are provided for the positioning of a rope or tape.These pulleys have a spiral or threaded groove in their conicalsurfaces. The

rope or tape has its ends fixed to the conical pulleys and is partlywound around the rope pulleys and disposed in the grooves. By thismeans, the torsional force of the grooves and the arrangement of therope pulleys is such such that with both pulleys rotating in the samedirection, the tendency of variation of the effective levers constitutedby the conical rope pulleys, are opposite to each other. Also, the drumon which the strip is wound is connected by gearing with the rope pulleyfrom which the rope is unwound. Furthermore, the drum from which thestrip is unwound is connected by gearing with the rope pulley onto whichthe rope is wound, and at least one torsion spring element is connectedinto the operative connection which is thereby formed.

As the rope falls into the grooves obliquely and can, under certaincircumstances, wear out, a further feature of the invention porvides anincrease in the reliability of operation. This is performed by havingone pulley so arranged that it can be displaced axially. A linearlymovable guide member is provided which is threadedly connected with therope pulleys. By this means, the rope pulleys are axially displacedrelative to each other in such manner that the rope does not rub on theedges of the grooves.

Additional objects and advantages of the present invention will becomeapparent upon consideration of the following description when taken inconjunction with the accompanying drawings in which:

FIGURE 1 is a diagrammatic perspective view of the present invention.

FIGURE 2 is a diagrammatic partial sectional view illustrating a simpledevice to provide for axial movement of one of the two rope pulleys.

FIGURE 3 is a diagrammatic perspective view of the cam of a furtherembodiment of the invention.

FIGURE 4 is a diagrammatic side elevational view of the cam togetherwith the rope pulleys.

FIGURE 5 is a diagrammatic plan view of the cam together with the ropepulleys.

Wit-h more particular reference to the drawings, FIG- URE 1 illustratesan embodiment of the invention wherein a film strip 1 is wound on anddisposed between two cylindrical drums 2 and 3. The film strip 1 isstretched between the drums which are mounted on two rotatable shafts 4and 5. The strip 1 is a transparent film which has a map imprintthereon, although the details of the indicia of the map are not shown. Abug or other type of marking device can be moved in the direction of thedouble arrow 6 to indicate the position of a vehicle or the like on themap. The bug is not shown. If the vehicle moves on the map at a rightangle to the direction of arrow 6, the two drums are rotated accordinglyso that the correct portion of the map is placed under the bug. For anexact indication, it is necessary that the film with the map thereondoes not flutter, even though the entire apparatus may vibrate. Thetensile must not fall below a predetermined minimum value at any time.

Two identical gearing arrangements 7 and 8 are connected with shafts 4and 5, respectively. The driving shafts 9 and 10 of these gears reducethe rotations of these shafts 4 and 5. The direction of rotation of thedrive and driven shaft is the same. A conical pulley 11 is mounted onshaft 9 and an identical pulley 12 is loosely mounted on shaft 10.Pulley 12 can thus rotate about the shaft 10. A disc 13 is fixed to theshaft 10 and has an eccentric pin 14 mounted thereon. A torsion spring16 is connected between this pin 14 and a corresponding eccentric pin 15mounted on the smaller end of rope pulley 12.

A groove 17 is provided in each of the rope pulleys and this grooveextends from one end to the other and has a clockwise spiral orright-hand thread. These grooves serve for guiding the rope 18 which isconnected to the end of the grooves. The rope is connected to the largerdiameter ends of the cones. Those grooves which are filled with rOpe areindicated 19. The rope is fastened to the rope pulley 11 at point 20.The gearing ratio of the gears 7 and 8 and the pitch of the grooves areadjusted in such manner that the radii 21 and 22 of the drums 2 and 3,respectively, and the radii of the grooves of the rope pulleys 11 and 12from which and into which the rope is wound, are always proportional.

The torsional force of the grooves and the arrangement of the ropepulleys is such that with both pulleys rotating in the same direction,the tendency of variation of the effective levers constituted by theconical rope pulleys, are opposite to each other.

Torsion spring 16 is under an initial stress and always applies momentsof rotation of equal magnitude on the rope pulley 12 and the disc 13.Thus, the pulley has the tendency to wind on more rope while the drum 3has a 3 tendency to Wind on more film. Since the drum 2 and the ropepulley 11 are connected to each other by the gearing '7, thesetendencies can not cause rotary movements but only a tensioning of themap strip 1 and the rope 18.

Movement of the rope pulleys and thus movement of the strip can only becaused by an outside moment of rotation. For this purpose, a DC. motor23 is provided which, via a gear 24, drives a gear 25 fixed to shaft 9.This motor is fed by two voltages V and V which are in series. Thevoltage V corresponds to the position coordinate in the direction ofmovement of the map and is supplied by a navigation calculator. Thevoltage V is a voltage provided from a potentiometer and which is tappedoff between the center tap and the wiper arm 26 of a potentiometer 27. Avoltage source 28 feeds the potentiometer while the wiper arm 26 isoperated by a toothed roller 29 which is in engagement with the edgeperforations 30 of the map strip 1. The dashed line 31 indicates amechanical connection between the toothed roller 29 and the wiper arm26. The motor 23 is arranged to rotate in a direction so that itdecreases its supply voltage continuously by means of the potentiometer27. When voltages V and V have the same value, the motor stops. In thismanner, the coordinate voltage V controls the position of the map strip1.

The sensitive driving system provides that the present invention doesnot have any residual moment. Starting from the stopped position of themotor at which V =V it is assumed that the vehicle or airplane whoseposition is to be indicated moves in the direction of the map strip 1.The navigation calculator, as a result, increases its output voltage VThus, a voltage difference is provided at the motor 23 and this causesthe motor to rotate shaft 9 in a direction which increases voltage V Therope pulley 11 and the drum 2 may thereby rotate in counter-clockwisedirection with the corresponding gear transmission ratio. This causesthe angular radius 21 to increase. On the other side, the angular radius22 decreases and to the same extent the effective lever on the ropepulley 12 decreases because the rope is wound on downwardly and theradius on which the rope is wound on pulley 12 decreases. The torsionspring 16 also rotates. However, this occurs without the ends thereofturning with respect to each other. The two opposite tensioning momentsmentioned above and produced by this spring always remain equalindependently of the change of the angular radii.

FIGURE 2 illustrates a schematic view of two rope pulleys 40 and 41 inthe form of truncated cones. In use, they correspond exactly to the ropepulleys shown in FIGURE 1 although the details of the drive are notshown in FIGURE 2. The two rope pulleys 40 and 71 are fixedly connectedwith coaxially extending threaded lugs 42 and 43, respectively. Thethreads of these lugs are shown as simple lines. Points 44 and 45 areshown in this figure to indicate that the rope pulley 40 can not move inaxial direction. However, the rope pulley 41 is arranged on a shaft 46which can be displaced in its bearings 47 and 48. A connecting member 49is provided which has two threaded openings into which the threaded lugs42 and 43 are disposed.

The pitch of the thread on the lugs 42 and 43 and the pitch of the ropegrooves 50 are the same. Therefore, the angle at which is formed betweenthe rope segment 51 and a line projected at right angles to the axes oflugs 42 and 43 at the point where the rope intersects with the axis oflug 42, remains constant independently of the position of the rope. Itis therefore possible to adjust the angle a in such manner by adjustingthe rope pulleys suitably before the rope is placed onto and fixed inthe pulleys, that the rope will not rub on the edges of the grooves,since these edges might be sharp and in any event wearing would occur.

Assuming that the device is positioned as shown in FIGURE 2, the rope ismostly wound on the pulley 41 While the pulley 40 is nearly empty ofrope. Assuming, now that the pulley 40 rotates twice in a direction towind rope onto this pulley, this then corresponds to one rotation ofpulley 41 in its unwinding direction since in the positions illustrated,the effective diameter of pulley 41 is twice that of pulley 40. Theconnection member 49 thus moves by two pitches (2/1) to the positionindicated in dashed lines. At the same time, the pulley 41 threadsitself by a movement equal to one pitch, out of the con= nection memberand attains the position indicated by dashed lines 52. However, duringthis time, the rope has moved on the pulleys in the direction of arrow53 and the movement has been an amount equal to two pitches on thepulley 40 and one pitch on pulley 41. This difierence in axial travel iscompensated for by the opposite axial movement of pulley 41 so that therope angle on is also maintained in the new position 52 of the pulley41.

The rope angle a is thus maintained during the entire winding andunwinding process, even though the ratio resulting from the rotaryspeeds of the two rope pulleys changes constantly. In the two endpositions in which the entire length of rope is wound on one of the twopulleys, the displaceable pulley 41 is in the position 52a shown indashed lines. Starting from this position, it moves into the position52b shown in dashed lines and then back to position 52a without changingthe direction of winding. Position 52b corresponds to the middleposition of the rope, that is, when the rope has an equal length woundon each pulley.

Since the pitch angle of the rope grooves is different at each point,contrary to what occurs in a cylindrical thread, the rope angle on willpreferably be adjusted to a medium value between the largest and thesmallest pitch angle and this compromise of pitch angle can be seen fromthe example shown in FIGURE 2 The embodiment shown in FIGURES 3 through5 above all provides a considerable saving in space. In this embodiment,the thread lugs are eliminated and a threaded type of connection isprovided by means of a double cam which directly engages the ropegrooves. This cam is shown in FIGURE 3 and includes two halves which arepivotally connected by a shaft 60. One half of this cam can be displacedalong two guide bars 61 and 62 and includes two longitudinal girders 63and 64 connected to each other by a bridge, the end 65 of which can beseen. The two guide bars pass through the lon gitudinal girders.

A lever 66 is mounted on the shaft 60 and a tension spring 67 isconnected to the other end of lever 66. Therefore, the cam half 68 has atendency to tilt upwardly toward the right as viewed in FIGURE 3 sincethis cam part is fixed to shaft 60 which is mounted for rotationalmovement in girders 63 and 64. Cam portion 68 is provided with tworidges 69 which are elongated and have rounded upper ends and aredesigned to engage in the empty grooves of the rope pulley 70.Corresponding ridges are provided on the bridge 65 although they are notvisible in FIGURE 3. They are, however, indicated at 71 in FIGURES 4 and5.

FIGURES 4 and 5 illustrate the double cam in a simplified manner andalso illustrate the rope pulleys 70 and 72 as well as the rope 73 whichis disposed about the pulleys. Pulley 72 can not be moved in axialdirection whereas the pulley 70 can be displaced on its shaft (notshown) in the direction of double arrow 70'. The guide bars 61 and 62are fixedly mounted to be parallel to the opposing surfaces of the twocones. By having the ridges 71 displaced relative to the ridges 69 inthe direction of the guide bars, these ridges can then engage intogrooves of the two rope pulleys which are free of the rope, even thoughthe rope runs over the double cam.

The functioning corresponds to the embodiment of FIGURE 2. If the pulley70 moves axially, then the distance between the surface lines of thecones changes. However, this is compensated for because the ridges 69are always spring-pressed into the grooves because of the spring 67 andthereby follow the movement of pulley 70.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes, andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

What is claimed is:

1. A device for maintaining the tensile stress of a strip stretchedbetween two drums, comprising, in combination:

two conical pulleys for positioning a rope and having spiral grooves intheir conical surfaces; a rope having its ends fixed to the conicalpulleys and partly wound about the rope pulleys in the grooves;

two drums having a strip stretched between them and Wound on the drums;and

gearing means for connecting the drum on which the strip is wound withthe rope pulley from which the rope is unwound, and the drum from whichthe strip is unwound with the rope pulley on which the rope is wound,and including means lfOI providing torsional biassing interposed betweenone of the drums and the pulley to which it is connected.

2. A device as defined in claim 1 wherein said pulleys are arranged withthe smaller end of one opposite the larger end of the other.

3. A device as defined in claim 2 wherein said rope is wound on thepulleys so that they rotate in the same direction.

4. A device as defined in claim 1 wherein said rope and pulleys arearranged so that both pulleys rotate in the same direction and thetendency of the effective levers of the rope pulleys are opposite toeach other.

5. A device as defined in claim 1 wherein one of said pulleys is mountedfor axial displacement.

6. A device as defined in claim 5 wherein said pulleys have threadedlugs projecting therefrom, and a connected member disposed between thelugs and into which the lugs are threaded.

7. A device as defined in claim 5 comprising a cam having a firstportion engaging the .grooves of one pulley and a second portionengaging the grooves of the other pulley.

8. A device for maintaining the tensile stress of a strip stretchedbetween two drums, comprising, in combina- .tion:

two conical pulleys for positioning a rope and having similar spiralgrooves in their conical surfaces with the large end of one pulleyopposite the small end of the other pulley;

a rope having its end fixed to the conical pulleys and partly woundabout each of the rope pulleys in the grooves thereof;

two drums having a strip stretched between them and wound on the drum;

means for maintaining a similar tangle of approach between the rope andthose grooves which the rope is entering regardless of where on thepulley such grooves are disposed; and

gearing means for connecting the drum on which the strip is wound withthe rope pulley from which the rope is unwound, and the drum from whichthe strip is unwound with the rope pulley on which the rope is wound,and including means for providing torsional biassing interposed betweenone of the drums and the pulley to which it is connected.

9. A device as defined in claim 8 wherein said means includes means formounting one of said pulleys for axial movement, and means connectedbetween said pulleys for causing said one pulley to move axially withrespect to the other upon rotation of said pulleys.

References Cited by the Examiner UNITED STATES PATENTS 2,376,777 1/1945Hornbostel 242- .5 3,233,843 2/ 1966 Dockstader 242-755 FOREIGN PATENTS708,792 5/ 1931 France.

FRANK J. COHEN, Primary Examiner. N. L. MINTZ, Assistant Examiner.

1. A DEVICE FOR MAINTAINING THE TENSILE STRESS OF A STRIP STRETCHEDBETWEEN TWO DRUMS, COMPRISING, IN COMBINATION: TWO CONICAL PULLEYS FORPOSITIONING A ROPE AND HAVING SPIRAL GROOVES IN THEIR CONICAL SURFACES;A ROPE HAVING ITS ENDS FIXED TO THE CONICAL PULLEYS AND PARTLY WOUNDABOUT THE ROPE PULLEYS IN THE GROOVES; TWO DRUMS HAVING A STRIPSTRETCHED BETWEEN THEM AND WOUND ON THE DRUMS; AND GEARING MEANS FORCONNECTING THE DRUM ON WHICH THE STRIP IS WOUND WITH THE ROPE PULLEYFROM WHICH THE